U.S. Fish and Wildlife Service Adult Pink Salmon Migratory Barriers and Habitat Utilization in the Dungeness River ADULT PINK SALMON MIGRATORY BARRIERS AND HABITAT UTILIZATION IN THE DUNGENESS RIVER by Roger J. Peters and Heather J. Tschaekofske U.S. Fish and Wildlife Service Western Washington Fish and Wildlife Office Fisheries Division Lacey, Washington September 2004 Abstract We evaluated potential migratory barriers and habitat use by adult summer pink salmon (Oncorhynchus gorbuscha) in the Dungeness River, Washington. Evaluation of migratory barriers involved monitoring four sites containing long, steep, shallow riffles, and collecting water temperature throughout the migration period. Habitat use was assessed by identifying holding locations of adult summer-run pink salmon using snorkeling techniques and measuring physical habitat characteristics at those locations. Habitat measurements included water depth, focal depth, water and focal current velocity, substrate, cover, and shade. Volunteers did not observe any adult pink salmon migrating through or holding at three potential physical barriers (long, steep riffles). These results may have been influenced by greater than normal late summer discharge which was due to greater than normal snow pack during the previous winter. Water temperatures were also cooler than those thought to result in significant migration delays. However, we observed pink salmon migrating during the daytime during our snorkel surveys. Adult pink salmon did not show a strong selection of different river habitat types. They preferred shaded or partially shaded areas to areas lacking shade. Adult pink salmons used cobble and gravel more than boulder and silt; however, use appeared to be similar to substrate availability. Numbers of holding adult pink salmon were positively influenced by the surface area of cover classified as in-stream objects, which provided shelter from current velocities. However, this relationship explained little of the overall variation in numbers of holding pink salmon. Adult pink salmon used areas with cover more than areas lacking cover. Adult pink salmon generally held in water greater than 1 m deep, were generally close to the bottom, and within 1.5 m of cover. Mean column and focal velocities averaged 57.8 cm/s and 30.1 cm/s, respectively. i Table of Contents Page Abstract............................................................................................................................................ i List of Figures................................................................................................................................iii List of Tables ................................................................................................................................. iv Introduction..................................................................................................................................... 1 Study Area .................................................................................................................................. 2 Methods........................................................................................................................................... 4 Migratory Barriers ...................................................................................................................... 4 Habitat Utilization....................................................................................................................... 4 Results............................................................................................................................................. 7 Migratory Barriers ...................................................................................................................... 7 Habitat Utilization..................................................................................................................... 10 Discussion..................................................................................................................................... 17 Migratory Barriers .................................................................................................................... 17 Habitat Utilization..................................................................................................................... 19 Acknowledgements....................................................................................................................... 21 References..................................................................................................................................... 22 Appendix A................................................................................................................................... 25 ii List of Figures Page Figure 1. Study reaches in the Dungeness River where adult pink salmon habitat utilization was evaluated, and areas surveyed to evaluate potential migratory barriers.......................................................................................................... 3 Figure 2. Dungeness River discharge upstream of irrigation withdrawals during 1994-1996. ..................................................................................................................... 8 Figure 3. Average daily temperatures in selected reaches of the Dungeness River during our study. ............................................................................................................ 9 Figure 4. Maximum daily temperatures in selected reaches of the Dungeness River during our study. ............................................................................................................ 9 Figure 5. Total numbers of summer-run pink salmon holding over different dominant substrate classes. ......................................................................................................... 13 Figure 6. IOB surface area utilization by groups of holding summer-run pink salmon in the Dungeness River (1 outlier removed)................................................................ 15 iii List of Tables Page Table 1. Cover type and function categories used to evaluate the importance of cover to adult pink salmon in the Dungeness River (from Bovee 1986). ...................... 6 Table 2. Substrate classification and size categories used to evaluate the importance of substrate to adult pink salmon in the Dungeness River (from Bovee 1986).......................................................................................................... 6 Table 3. Total number of different habitat types sampled during this study. ............................. 10 Table 4. Total number of habitat types sampled in each study reach during this study. .............. 10 Table 5. Total number of fish of different species and size classes observed in each reach during each survey...................................................................................... 11 Table 6. Distribution of groups of summer-run pink salmon holding in different habitat types for each survey reach............................................................................... 11 Table 7. Number of groups of summer-run pink salmon observed holding in shade, no shade, and partial shade. .......................................................................................... 12 Table 8. Number and percent of groups of summer pink salmon holding above different dominant substrates........................................................................................ 12 Table 9. Percentages of different dominant substrates utilized by holding summer-run pink salmon for each survey reach. .............................................................................. 14 Table 10. Number and percent of groups of summer-run pink salmon holding above different subdominant substrates. .................................................................... 14 Table 11. Number of pink salmon groups observed holding near each cover type...................... 15 Table 12. Percentages of different cover objects by cover type utilized by holding summer-run pink salmon in the Dungeness River........................................................ 16 Table 13. Summary statistics for each of the habitat variables used by adult summer-run pink salmon in the Dungeness River........................................................ 17 Table A1. Summary statistics for water and focal depth utilized by holding summer-run pinks for each survey reach...................................................................... 25 iv List of Tables (continued) Page Table A2. Summary statistics for mean water and focal velocity utilized by holding summer-run pinks for each survey reach...................................................................... 25 Table A3. Summary statistics for distance to cover utilized by holding summer-run pinks for each survey reach. ......................................................................................... 26 Table A4. Summary statistics for relative depth utilized by holding summer-run pinks for each sampling reach. ..................................................................................... 26 v Introduction Dungeness River pink salmon (Oncorhynchus gorbuscha) populations have been depressed since the early 1970s, with the fall run designated in critical status (WDF et al. 1993). Population trends of pink salmon in the Dungeness River were consistent with overall Puget Sound pink salmon trends